1. Field of Invention
The present invention relates to the configuration of a substrate on the side of reflecting electrodes which constitutes a reflective-type liquid crystal panel and to a liquid crystal panel using the substrate, and further to an electrode apparatus using the liquid crystal panel.
2. Description of Related Art
Use of transmissive-type liquid crystal panels has been implemented as microminiature a high-definition active matrix liquid crystal panels which are suitable for light valves for projectors or the like, in which thin film transistors (TFTs) are formed on a quartz substrate using polysilicon, and transparent electrodes are formed thereon as pixel electrodes. In the transmissive-type liquid crystal panel using the TFT, since TFT regions provided for the individual pixels, gate electrodes for driving the TFTs, and wiring regions constituting source and drain electrodes are not transmissive regions for transmitting liquid, as the panel resolution increase such as XGA and SXGA, the aperture ratio decreases, which is a fatal detect.
Accordingly, as active matrix liquid crystal panels which can be easily fabricated with a high aperture ratio in comparison with the transmission-type active matrix liquid crystal panels, reflective-type active matrix liquid crystal panels have been proposed, in which pixel electrodes are made as reflecting electrodes and transistors are arranged thereunder. FIG. 9 is a sectional view of a conventional reflective-type active matrix liquid crystal panel, around a scribe line surrounding the exterior of the pixel and peripheral circuit regions. In FIG. 9, numeral 101 represents a p-type semiconductor substrate such as single crystal silicon and numeral 102 represents a p-type well region, having a higher impurity concentration than that of the substrate, formed on the surface of the semiconductor substrate 101. Numeral 102 represents a field oxide film for isolating elements formed on the surface of the semiconductor substrate 101, and numeral 114 represents a gate oxide film formed by thermal oxidation of the surface of the silicon substrate. A first interlayer insulating film 104 is formed on the field oxide film 103 and the gate insulating film 114. On the first interlayer insulating film 104, a first conductive layer 10a, which has been formed simultaneously with a source electrode, is formed. A second interlayer insulating film 108 is formed on the first conductive layer 107a, a second conductive layer 120 is formed as a guard ring on the second interlayer insulating film 108, and the guard ring 120 is connected to the first conductive layer 107a through a via opening formed in the second interlayer insulating film 108. A third interlayer insulating film 110 is formed on the second conductive layer 120, and a third conductive layer 113 formed on the third interlayer insulating film 110 is connected to the second conductive layer 120 through a via opening formed in the third interlayer insulating film 110. An oxide film 111 and a silicon nitride film 121 are formed further thereon.
In the conventional reflective-type active matrix liquid crystal panel described above, a device substrate on which reflecting electrodes are formed must be provided with a passivation film as a protection film having moisture resistance in order to ensure reliability of transistors and wiring metals on the element substrate.
Therefore, is most cases, as shown in FIG. 9, as a passivation film for a element substrate, a silicon nitride film 121 formed by a reduced pressure CVD method or the like is used. As shown in FIG. 9, since the side is exposed when the element substrate is diced, a guard ring 120 which connects all the metal wiring layers is often provided in the periphery of the element. Moisture penetration from the surface of the element substrate can be prevented by the passivation film, and moisture penetration from the dicing side can be prevented by the guard ring.
With respect to the passivation film formed by a CVD method, current techniques cannot prevent the occurrence of uneven thickness of approximately 10%. In the reflective-type liquid crystal panel, if a silicon nitride film forming by a CVD method is used as a passivation film, since the silicon nitride film has a larger refractive index than that of a liquid crystal, because of the inconsistency of the thickness of the silicon nitride film, the reflectivity in the visible light range may vary greatly, which is disadvantageous. Therefore, in the reflective-type liquid crystal panel, the passivation film must be nonexistent or must have a thickness of at most several tons of nanometers.
In a typical liquid crystal panel, a flexible printed circuit (FPC) is used for connecting an element substrate to an external circuit. The FPC contains conductive particles, and the terminal of the element substrate and the terminal of the FPC are connected to each other through the conductive particles. However, if a passivation film is nonexistent on a guard ring of the element substrate or if it is thin, the conductive particles are connected to the guard ring, resulting in short-circuiting between adjacent terminals through the guard ring, which is disadvantageous.